In a wireless communication system, a packet is transmitted on a radio channel. In view of the nature of the radio channel, the packet may be distorted during the transmission. To receive the signal successfully, a receiver should compensate for the distortion in the received signal using channel information. Generally, to enable the receiver to acquire the channel information, a transmitter transmits a signal known to both the transmitter and the receiver and the receiver acquires knowledge of channel information based on the distortion of the signal received on the radio channel. This signal is called a pilot signal or a Reference Signal (RS). In case of data transmission and reception through multiple antennas, knowledge of channel states between Transmission (Tx) antennas and Reception (Rx) antennas is required for successful signal reception. Accordingly, different RS sequences should be configured for the respective Tx antennas.
FIG. 1 illustrates an uplink subframe structure in a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE). Referring to FIG. 1, the horizontal axis represents frequency and the vertical axis represents time. Data is transmitted on a subframe basis and one subframe includes two slots each having six or seven symbols. An RS sequence occupies one symbol in each slot. The RS sequence is transmitted across an allocated total frequency band.
In the LTE system, a plurality of User Equipments (UEs) communicate with an evolved Node B (eNode B or eNB) in Spatial Division Multiple Access (SDMA). For the SDMA communication with the eNB, each of the UEs generates an RS sequence based on a control signal received from the eNB and transmits the RS sequence to the eNB.
To allow the eNB to stably decode the RS sequences received from the UEs, the RS sequences should be mutually orthogonal or have small cross correlations with one another. As the LTE system supports only one antenna on an uplink, a UE transmits one RS at one time.
Compared to conventional wireless communication systems that support a single antenna on an uplink, future wireless communication systems are highly likely to support uplink data transmission from a UE through multiple antennas. For instance, a UE should transmit uplink RSs through up to four antennas in a Long Term Evolution??Advanced (LTE??A) system. Accordingly, there exists a need for developing a method for transmitting a plurality of RSs from a UE.